In advanced processes (gate lengths of 0.35 .mu.m or less), the need has recently arisen to integrate EEPROM-type non-volatile memories in high-speed devices that use the technique of saliciding the diffusions. As known, this technique is based on the use of a layer of self-aligned silicide ("salicide" from "Self-Aligned Silicide"), which reduces the resistivity of the junctions. The layer of salicide (which typically comprises titanium, but can also be cobalt or another transition metal) is formed by depositing a titanium layer on the entire surface of the device, and performing a heat treatment that makes the titanium react with the silicon, which is left bare on the junctions and the gate regions, such as to form titanium silicide. Subsequently, the nonreacted titanium (for example that deposited on oxide regions), is removed by etching with an appropriate solution, which leaves the titanium silicide intact. Thereby, both the gate regions and the junctions have in parallel a silicide layer with low resistivity (approximately 3-4 .OMEGA./square), which reduces the series resistance at the transistors. The salicide technique is described for example in the article "Application of the self-aligned titanium silicide process to very large-scale integrated n-metal-oxide-semiconductor and complementary metal-oxide-semiconductor technologies" by R.A. Haken, in J. Vac. Sci. Technol. B, vol 3, No. 6, Nov/Dec 1985.
The high voltages necessary for programming non-volatile memories (higher than 16 V) are however incompatible with saliciding the memory cells diffusions, since the breakdown voltage of the salicided junctions is lower than 13 V.
Process flows are thus being designed which permit integration of non-volatile memory cells and high-speed transistors with saliciding; however this integration is made difficult by the fact that these components have different characteristics, and require different process steps.